In automotive vehicles, a brake event signal is used as an input for various diagnostic routines included in on-board diagnostics (“OBD”) of the vehicle and also as an input for various control routines. A brake event signal as used herein means a signal that indicates that the brakes of the vehicle are being applied or are being released. The vehicle's OBD is implemented in one or more electronic control units in the vehicle, such as in an electronic control unit of the vehicle's engine management system. Control routines that control various aspects of the vehicle are also implemented in one or more electronic control units of the vehicle. By way of example and not of limitation, control and diagnostic routines that use the brake event signal as an input include misfire target learning, air conditioner control, diagnostics management, diagnostics management (freeze frame reporting), electric vacuum pump diagnostics, steering angle diagnostics.
Heretofore, a brake pedal position signal or a master cylinder pressure signal has often been used as the brake event signal. The brake pedal position signal is a signal that indicates the position of the brake pedal, such as along a travel range from fully depressed to fully released. The master cylinder pressure signal is a signal that indicates a pressure of brake fluid in the master cylinder. It should be understood that this pressure can be indicative of the pressure in any chamber of the master cylinder that is pressurized when a driver applies the brakes of the vehicle by pushing the brake pedal.
Modern vehicles are typically equipped with anti-lock braking systems that include an electronic control unit and hydraulics for preventing the brakes from locking when they are being applied. In some cases, the hydraulics are operable independently of the master cylinder to apply the vehicle's brakes. The control of the anti-lock braking system is often included in an electronic stability control system of the vehicle either as a separate anti-lock braking electronic control unit or as part of an electronic control unit of the electronic stability control system.
In vehicles having certain types of autonomous driver assistance systems, the autonomous driver assistance system has autonomous braking events in which the autonomous driver assistance system automatically causes the vehicle's brakes to be applied without the driver having pressed the brake pedal. It does so by causing the vehicle's brakes to be applied by the anti-lock braking system in which the hydraulics are operable independently of the master cylinder to apply the brakes. An autonomous braking event is a braking event that occurs when the autonomous driver assistance system determines that the vehicle should be braked and causes the vehicle's brakes to be applied without a driver pressing the brake pedal. One example of an autonomous driver assistance system having an autonomous braking event is adaptive cruise control where a vehicle having its cruise control active is automatically slowed as it approaches a vehicle in front of it, in some cases by the automatic application of the vehicle's brakes by the autonomous driver assistance system.
The electronic control unit of the anti-lock braking system provides a brake torque signal indicative of the amount of brake torque being applied during braking of the vehicle. It should be understood that brake torque signal in this context can be an analog signal having a level indicative of the brake torque or a digital value indicative of the brake torque being applied. In normal braking when the driver has depressed the brake pedal, the master cylinder provides pressurized brake fluid to the brakes to apply them. The master cylinder pressure signal is provided to the electronic control unit of the anti-lock braking system which uses it to determine the brake torque and generate the brake torque signal. In cases where the brakes are being operated by the anti-lock braking system either in an anti-lock braking action or in an autonomous braking event, the electronic control unit of the anti-locking braking systems determines the brake torque to be applied and generates the brake torque signal accordingly.
In autonomous driver assistance systems having autonomous braking events, the brake pedal position signal and the master cylinder pressure signal do not indicate all braking events as the autonomous braking events occurs independently of a driver pressing the brake pedal. When this occurs, the hydraulics of the anti-lock braking system operate independently of the master cylinder to apply the brake and in these situations. Thus, there is not a brake pedal position signal indicating that the brake pedal has been depressed or a master cylinder pressure signal indicative of pressurized brake fluid in the master cylinder.
In OBD diagnostics, a component must typically fail the diagnostic multiple times for the OBD diagnostic to set a fault code for that component, and typically set an alert such as illuminating the “check engine” light in the vehicle. To prevent false failures, the inputs to the diagnostic routines of the OBD are required to be rationalized before they can be used by the applicable diagnostic routines. That is, each input of a sensed a condition must be compared against another input of a sensed similar condition at essentially the same time and the two inputs must correlate with each other for the rationalization of the input to be determined to be successful.
FIG. 1 is a simplified block diagram of a prior art vehicle 100 having an engine management system referred to herein as EMS 102 and an electronic stability control system referred to herein as ESC 104. EMS 102 includes an EMS electronic control unit referred to herein as EMS ECU 106. ESC 104 includes an anti-lock braking system electronic control unit referred to herein as ABS ECU 108. It should be understood that ABS ECU 108 could be part of an electronic control unit (not shown) for ESC 104. ABS ECU 108 provides brake torque signal 110 as an input to EMS ECU 106. EMS ECU 106 also has an inputs a brake pedal position signal 112 and a master cylinder pressure signal 114.